Securing ASP.NET with web.config

Published 01/06/02

Introduction

In web.config we looked at what web.config is and I told you that I would talk more about it in other articles so here is one. This article will look at security in your ASP.NET applications and how to secure your applications. See Security in ASP.NET for more information on security in ASP.NET.

web.config

web.config does most of the work for you as it tells the application the who, what, where, when and how to be authenticated (it doesn't need to tell it why).

<configuration> <system.web> <authentication mode="mode"> </authentication> </system.web> </configuration>

This is the beginnings of something bigger. The <authentication> tags and what goes between is everything ASP.NET needs to know to provide security. The 'mode' property is about how to authenticate, the possible values are - Windows, Forms and Passport.

Note : <authentication> only works in the root folder of the virtual directory's web.config, not subfolders.

Forms

Forms security works so that you don't have to create new Windows accounts to let people in. I won't go over how it works (see Security in ASP.NET). Here is the configuration -

<configuration> <system.web> <authentication mode="Forms"> <forms name="Auth" loginURL="login.aspx" protection="All" timeout="10" /> </authentication> </system.web> </configuration>

When you are authenticated you are given a cookie called 'Auth'. The place where you login is called login.aspx. The protection is by default - All, this gives the cookie validation (to make sure it hasn't been tampered) and encryption (using Triple-DES or DES), you can modify this with different properties (All, None, Encryption, Validation). Next the timeout sets when the user's login will time-out (the default in 30) in minutes.

Before we continue lets set up our login.aspx file -

<script language="VB" runat="server" /> Sub btn_click(sender as object, e as eventargs) 'You may want a database connection or something here 'To provide authentication from a database If uname.Text = "philipq" And pword.text = "password" Then FormsAuthentication.SetAuthCookie(uname.text, true) Response.Redirect("seethis.aspx") Else lblmsg.Text = "Invalid username or password" End If End Sub </script>

I'll leave you to put the server controls in.

All this does is check the values of the two textboxes (uname and pword) and if they're fine it sets Formsauthentication.SetAuthCookie() to validate the user. the SetAuthCookie method takes two parameters - the username of the authorized user and weather or not to keep the cookie after the user closes the browser. The FormsAuthentication provides many other useful methods.

So far we have given simple authentication for users and the data is automatically encrypted. The cookie is also encrypted like this -

aucookie
E605AB187FED02216B161C9EDC5F64B4F51ECA418DE3E1FE11EAFFD108D4B05F9949B4490C692615443A01F8ABA0E7E1CEA2F1C9B9D8EB067198C954A3EE85E6
localhost/
1024
3450704256
33137864
3627820272
29464168
*

You can clearly see the name of the cookie and the server it got it from.

U/P Storage

There is another way to get username and password data rather than from a database or what we did before. By using the <credentials> tag we can provide usernames and passwords for users.

<credentials passwordFormat="Clear"> <user name="philipq" password="password" /> </credentials>

This goes within the <authenticate> tags and you can just add more users and needed. The passwordFormat can be Clear, MD5 or SHA1 which is the format that the passwords are encrypted in.

You then have to modify your login.aspx code like this -

<script language="VB" runat="server" /> Sub btn_click(sender as object, e as eventargs) If FormsAuthentication.Authenticate(uname.text, pword.text) Then FormsAuthentication.SetAuthCookie(uname.text, true) Response.Redirect("seethis.aspx") Else lblmsg.Text = "Invalid username or password" End If End Sub </script>

The Authenticate method takes in the username and password and returns true or false.

Summary

There is a lot more to security than just this. You can also have role based security, path based security and more with other tags as well as the <authorize> tag. But I can't include it all here there is plenty of information in the .NET Framework SDK as well as other sites out there on security using <authenticate> and <authorize>. For more information on security in ASP.NET see Security in ASP.NET.